1. Field of the Invention
This invention relates to an integrated optical circuit element for realizing a functional element such as a light deflector or a light modulator and to a method of making the same.
2. Description of the Prior Art
As a method of introducing a light from outside into a wave guide forming an integrated optical circuit or leading the light propagated through the wave guide out of the wave guide, there is known a prism coupler, a butt coupler for introducing a light from the polished end surface of a wave guide directly into the wave guide, etc. The prism coupler is simplest in construction, but prisms are expensive and when the prisms are to be coupled together, a jig or the like for urging the prisms against the wave guide juts out from the integrated optical circuit element, and this provides a great impediment in making the element small in size and low in cost. On the other hand, to introduce a light directly into the end surface of the wave guide by a butt coupling, it is necessary to set the light in the end surface of the wave guide at accuracy of the order of sub-microns and this makes it unavoidable to use a very expensive movable rotatable stage capable of effecting fine adjustment in the directions of three x, y and z axes. Also, polishing of the end surface of a thin substrate is difficult and expensive. Accordingly, like the prism coupler, the butt coupler is not desirable for realization of small and inexpensive elements.
As a means for overcoming the above-noted disadvantages, a photocoupler utilizing a planar type diffraction grating has been proposed (M. L. Dakss et al., Applied Physics Letters 16(12), 523 (1970): Grating Coupler For Efficient Excitation of Optical Guided Waves in Thin Films). An example of a light deflector using such diffraction grating type photocouplers is shown in FIG. 1 of the accompanying drawings. In FIG. 1, there is formed on a substrate 1 a wave guide 2 having a refractive index higher than that of the substrate, and diffraction grating type photocouplers 3.sub.1 and 3.sub.2 are formed in the wave guide 2. An incident light 4 having entered at a suitable angle is introduced into the wave guide 2 by the photocoupler 3.sub.1, is propagated therethrough as a propagated light 5 and is led out of the wave guide as an emergent light 6 by the photocoupler 3.sub.2. An MTS array (multiple tilted SAW transducer array) 7 comprising a plurality of interdigital transducers (hereinafter referred to as IDTs) which generate surface acoustic waves (hereinafter referred to as SAWs) different in wavelength is formed on the wave guide 2. When RF power is supplied to the MTS array 7 to excite SAWs 8 from the respective IDTs and the propagated light 5 is Bragg-diffracted, a diffracted light 9, like the emergent light 6, is led out of the photocoupler 3.sub.2 and this can be used, for example, for the switching between two levels.
The construction of the diffraction grating type photocoupler in the integrated optical circuit element of the prior art as described above will now be described by reference to FIGS. 2A and 2B of the accompanying drawings. FIGS. 2A and 2B correspond to the cross-section taken along the line A-A' in FIG. 1. In the example shown in FIG. 2(A), a wave guide 12 is formed on a substrate 11 and grids 10 formed, for example, of a dielectric material are mounted on the wave guide 12 to thereby form a diffraction grating. However, such a mounted type photocoupler has suffered from a disadvantage that the coupling efficiency of light, namely, the rate of the light introduced into the wave guide to the incident light or the rate of the emergent light to the propagated light, is very low.
Also, in the photocoupler shown in FIG. 2(B), a wave guide 22 formed of a photosensitive material is formed on a substrate 21 as by sputtering and a part of the wave guide is exposed to light to thereby make a volume type diffraction grating. An integrated optical circuit element using such a photocoupler can obtain a coupling efficiency higher than that obtained by the example of FIG. 2(A), but has suffered from a disadvantage that the wave guide is liable to peel off the substrate or the photosensitivity of the wave guide may vary with time and the element does not stand long use.
Further, in the integrated optical circuit elements of the prior art as shown in FIGS. 2(A) and 2(B), when an electrode is to be formed on the wave guide like the MTS array 7 of FIG. 1, for example, it must be formed independently of the photocoupler, and this has led to an increased number of element manufacturing steps and an increased cost of manufacture.